The drive for reduced cost per unit wafer processed characterizes the semiconductor industry. Thus the semiconductor industry continuously searches for ways to increase wafer output and/or reduce overall equipment costs (costs of ownership). Among the factors significantly affecting cost of ownership for a given piece of equipment are clean room costs, footprint and labor costs. It is well recognized that overall semiconductor wafer fabrication system (i.e., fabrication tool) productivity increases are achieved by ensuring a constant supply of wafers at each tool. Conventionally this has been accomplished by employing a local buffer supply (i.e., a supply of wafers at the tool). For example, the "MINI BUFFER" marketed by Jenoptik/Infab is a vertical buffer which is positioned near a fabrication tool's load lock chambers. The MINI BUFFER comprises a series of vertically arranged shelves and one or more load ports for access by the tool's loader robot, and/or for access by factory transport agents (i.e., the mechanism that transfers wafer carriers from the factory to the buffer apparatus' factory load port). Conventionally one MINI BUFFER is positioned near each load lock, a distance from the load lock sufficient to accommodate the axis of rotation of a front loader robot. The loader robot may then access either MINI BUFFER to obtain a wafer carrier for loading to either load lock. Although such methods maintain a constant local buffer supply of wafer carriers, they occupy a considerable amount of floor space thus increasing the system's cost of ownership. The fact that fabrication tools are frequently maintained in a clean room environment further exacerbates the increased cost associated with the system's larger footprint.
In addition, most prior art systems do not allow simultaneous access by the tool loader and the factory transport agent, and thereby complicate factory transport scheduling.
A related, commonly-assigned application Ser. No. 08/764,661 discloses a Factory Automation Apparatus and Method for Handling, Moving and Storing Semiconductor Wafer Carriers. Application Ser. No. 08/764,661 provides an apparatus which advantageously allows for independent operation of the factory transport agent and the fabrication tool's loader mechanism, and provides for local interconnection of fabrication tools in a reduced footprint configuration. However, a continuous need exists for an apparatus and method which provides even further footprint reduction.